I would definitely use this, given we don't currently have many good
options for querying against the database and getting non-ActiveRecord
objects back.
I often want a fast way to serialize stuff as JSON (ie. without
instantiating AR objects and then turning them back into hashes), and doing
this using `select_values` is pretty cumbersome.
For example: `render json: { tasks: current_user.tasks.hash_pluck(:id,
:name, :completed) }`
That said, I'd probably favour a more general way to query the database and
get back arrays/hashes over something like `hash_pluck`, which would only
handle very simple cases.
On Saturday, June 27, 2015 at 4:35:30 AM UTC+10, Al Tenhundfeld wrote:
>
> The proposed method has more benefit when plucking multiple columns. Of
> course, you can still do pluck(:first, :last, :dob).map {|e| {first: e[0],
> last: e[1], dob: e[2]} }, but I guess that's a little cumbersome and
> smelly. I'm not arguing the benefit – small benefit IMO – is worth the cost
> of adding and maintaining for years, but I do see its convenience.
>
> -Al
>
> On Thu, Jun 25, 2015 at 5:39 PM, Ryan Bigg <[email protected]
> <javascript:>> wrote:
>
>> What is the benefit of this method?
>>
>> You can pluck(:firstname).map { |e| { firstname: e } } if you really
>> wanted that. Why are you plucking and wanting it to be a hash?
>>
>>
>>
>> On 25 Jun 2015, at 19:59, Mike Campbell <[email protected]
>> <javascript:>> wrote:
>>
>> The regular AR pluck method returns the values only, for instance:
>> Student.pluck(:firstname) => ["John", "Mike", "Simon"]
>>
>> It'd be a nice feature to have a version which returns a hashes with the
>> column names as keys: [{ firstname: "John"}, { firstname: "Mike" }, {
>> firstname: "Simon" }]
>>
>> I know this can (almost) be achieved with
>> Student.select(:firstname).map(&:attributes) (it forces you to have an id
>> attribute), but this involves instantiating lots of AR objects, which loses
>> the benefit of pluck.
>>
>> An example implementation would be:
>>
>> def self.hash_pluck(*keys)
>> pluck(*keys).map{ |vals| Hash[keys.zip(Array(vals))] }
>> end
>>
>> In some (probably bad) benchmarks I made comparing this to the select
>> alternative, the select method was ~3.4x slower.
>>
>> Benchmark.ips do |x|
>> x.report("hash_pluck") { Student.hash_pluck(:firstname) }
>> x.report("select") { Student.select(:firstname).map(&:attributes) }
>> x.compare!
>> end
>>
>> Calculating -------------------------------------
>> select 6.000 i/100ms
>> hash_pluck 24.000 i/100ms
>> -------------------------------------------------
>> select 77.096 (±29.8%) i/s - 342.000
>> hash_pluck 265.316 (±41.8%) i/s - 1.104k
>>
>> Comparison:
>> hash_pluck: 265.3 i/s
>> select: 77.1 i/s - 3.44x slower
>>
>> Just thought that it might be a nice convenience method to have!
>>
>> Cheers,
>> Mike
>>
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